Thin film manufacturing method and manufacturing apparatus, and thin-film transistor and manufacturing method

ABSTRACT

A method of fabricating a thin film includes: forming, on a substrate, a thin film with film properties varying from region to region on the substrate, by selectively heating the substrate; and patterning the thin film in a predetermined pattern by etching the thin film to selectively remove only a portion of the thin film with specified film properties. The method reduces the fabrication process temperature and the number of fabrication steps, while inhibiting degradation in device performance.

TECHNICAL FIELD

[0001] The present invention relates to a method and apparatus forfabricating a thin film, and a thin film transistor used in liquidcrystal display devices, organic EL devices, and the like as theswitching element or the like, and a method of fabricating such a thinfilm transistor.

BACKGROUND ART

[0002] A hydrogenated amorphous silicon thin film (hereinafter referredto as a-Si:H thin film) has been put to practical use as a pixelswitching transistor for liquid crystal displays, as an optical sensorserving as an image sensor for facsimile machines, as a solar cell usedas a battery for calculators, and the like. The biggest advantage ofthis a-Si:H thin film is that the film can be fabricated stably on alarge-area substrate with good reproducibility at a process temperatureof only about 300° C. However, with an increase in pixel density inliquid crystal displays and image sensors, silicon semiconductor thinfilms compatible with a faster drive have been demanded. Conventionaltransistors using an a-Si:H thin film had a mobility of 1.0 cm²/V·sec atmost, and thus did not have sufficient performance to satisfy thedemand. Thus, in order to improve mobility, development of techniquesfor crystallizing a-Si:H thin films has been pursued. Methods for thecrystallization include, for example, the following techniques.

[0003] 1) Depositing a thin film on a substrate by plasma enhanced CVD,using a source gas in which hydrogen or SiF₄ is mixed in silane gas, andthen crystallizing the thin film.

[0004] 2) Using an a-Si thin film as a precursor, attempting tocrystallize the a-Si thin film.

[0005] Of these techniques, the crystallization method described in thetechnique 2) includes, for example, a solid phase growth technique, inwhich heat treatment is performed at about 600° C. for an extendedperiod of time, and an excimer laser annealing technique.

[0006] With, in particular, the latter excimer laser annealingtechnique, a polycrystalline silicon thin film with high mobility (>100cm²/W·sec) has been successfully obtained without the need to activelyincrease the substrate temperature. This fact is described in detail,for example, in IEEE Electron Device Letters, 7 (1986), pp. 276-278 andIEEE Transactions on Electron Devices, 42 (1995), pp. 251-257.

[0007] When a TFT of the above-described a-Si:H thin film orpolycrystalline silicon thin film is used, as the switching transistor,in the pixel portion of a liquid crystal display, an ON current isrequired which is sufficient to write signals applied to the TFT to theliquid crystal (layer) within a given time period, and in addition areduction of leakage current in an OFF state is required. Further, in abuilt-in type liquid crystal display having a drive circuit provided onthe periphery of the substrate, when a TFT of the polycrystallinesilicon thin film is used in the drive circuit, the performance andreliability of each TFT need to be sufficiently assured as a circuitelement.

[0008] In order to satisfy these requirements, for example, in a TFThaving an a-Si:H thin film, the source region and the drain region aredoped with impurities so as to reduce leakage current- In addition, in aTFT having a polycrystalline silicon thin film, an offset structure oran LDD structure is employed so as to maintain the performance andreliability of the TFT, and at the same time, to reduce so-calledleakage current in an OFF state. (Note that the term “offset structure”refers to a structure in which appropriate space (for example, 0.5 μm)is provided between the channel portion (which is located immediatelybelow the gate electrode in the case of a top-gate type TFT) and each ofthe source and drain regions of the semiconductor, and that the term “DDstructure” refers to a structure in which between the channel portion(which is located immediately below the gate electrode) and each of thesource and drain regions of the semiconductor a doping region isprovided in which impurities with a lower concentration than those ofthe source and drain regions are diffused.)

[0009] Future demands in, for example, liquid crystal displays would befor low cost and image quality (for example, a display grade having aresolution such as that of photo image quality), and the like. Forsatisfying such demands, very fine pixels and fast operation of anin-built drive circuit are, of course, required in liquid crystaldisplays, and technically, fabrication of an extremely small TFT becomesan important and essential technique.

[0010] If an extremely small TFT is realized, it is possible in, forexample, a TFT used in the pixel portion (hereinafter referred to as TFTfor a pixel) to further increase the aperture ratio of the pixel, reducethe capacity level of parasitic capacity, improve image quality, andincrease driving speed. In addition, in a TFT used in an in-built drivecircuit (hereinafter referred to as TFT for a drive circuit), thecapacity level of parasitic capacity is reduced, achieving an evenfaster drive.

[0011] Note, however, that fabrication of an extremely small TFT isaccompanied by other problems to overcome. One of the problems in viewof the TFT for a pixel is that it is necessary to further reduce aleakage current in an OFF state of about 10⁻¹² A, which isconventionally obtained, by one digit or more to reduce the brightnessdifference in the plane of the panel. If this problem is not overcome,even if an extremely small TFT reduces an area per pixel and a storagecapacity portion for storing an electric charge of signals, it becomesdifficult to realize a bright display without causing a reduction inaperture ratio. In addition, as for the foregoing problems in view ofthe TFT for a drive circuit, in employing the above-described offsetstructure or LDD structure, factors in fabrication such as fineprocessing accuracy and alignment accuracy for photolithography becomecritical limitations. Further, since the offset structure and the LDDstructure require stable characteristics and also require the structureto be self-aligned, the fabrication process becomes more complicated,causing an increase in costs.

[0012] Moreover, a TFT for a pixel or a TFT for a drive circuit used inliquid crystal displays, a display and image-input integrated panel, anoptical sensor serving as an image sensor used in facsimile machines, asolar cell used as a battery for calculators, or the like is expected tobe developed, with use of a flexible substrate (made of plastic or thelike), to a ultra-thin flexible input and output panel capable ofconnecting to an electronic paper and a network (Internet). Thus, such aflexible substrate also requires techniques for fabricating a thin filmtransistor, an optical sensor, a solar cell, and the like with excellentcharacteristics at low cost.

[0013] However, provision of TFTs and the like on the flexible substraterequires techniques for fabricating extremely small TFTs on the flexiblesubstrate and improvement in reliability. In addition, because theflexible substrate is inferior in heat resistance to, for example, aglass substrate, the fabrication process temperature needs to bereduced. Moreover, in order to cut fabrication cost, the number offabrication steps needs to be reduced.

[0014] To summarize the above, conventional TFTs have problems describedbelow.

[0015] (i) A complicated fabrication process and an increase in costsresulting from the fabrication of extremely small TFTs.

[0016] (ii) A reduction in reliability of TFTs resulting from thefabrication of extremely small TFTs.

[0017] (iii) A high process temperature upon formation of TFTs on aflexible substrate or the like.

DISCLOSURE OF THE INVENTION

[0018] The present invention has been made so as to overcome theforegoing and other problems. An object of the present invention is toreduce the fabrication process temperature and the number of fabricationsteps, while inhibiting degradation in device performance.

[0019] (Methods of Fabricating a Thin Film)

[0020] (1) In order to overcome the foregoing problems, there isprovided a method of fabricating a thin film according to the presentinvention comprising: forming a thin film on a substrate, the thin filmwith film properties varying from region to region on the substratebeing formed by selectively heating the substrate; and patterning thethin film in a predetermined pattern by etching the thin film toselectively remove only a portion of the thin film with specified filmproperties.

[0021] With the above-described method, a reduction in processtemperature and a reduction in processing steps are achieved. That is,in forming a thin film according to the above-described method, theentire surface of the substrate is not heated but only a portion of thesubstrate necessary for film formation is selectively heated. Thus, asignificant increase in substrate temperature can be prevented, reducingthe process temperature.

[0022] In addition, the reason for selectively heating the substrate isto cause a temperature distribution on the substrate surface. In doingso, the temperature conditions vary from region to region on thesubstrate, and consequently a thin film with film properties varyingfrom region to region is formed on the substrate. For example, whenthere are formed, on the substrate, a region with a high temperature anda region with a low temperature by selectively heating the substrate, itis possible to vary the film properties between a portion correspondingto the region with a high temperature and a portion corresponding to theregion with a low temperature. Here, the variation in film propertiesappears as differences in the etching rate upon etching of the thinfilm. Specifically, in the comparison of the etching rate between theportion corresponding to the region with a high temperature and theportion corresponding to the region with a low temperature, the formerhas a lower etching rate. Therefore, even if the etching of the thinfilm is performed under the same conditions, only the portioncorresponding to the region with a low temperature is selectivelyremoved. Hence, according to the above-described method, a thin filmwith a predetermined pattern can be formed without using a mask, and theprocessing steps such as photolithography conventionally required can bereduced.

[0023] (2) In addition, in order to overcome the foregoing problems,there is provided another method of fabricating a thin film according tothe present invention comprising: depositing a thin film on a substrate,the thin film being deposited only in a specified region by selectivelyheating the substrate to vary a deposition rate from region to region onthe substrate.

[0024] With the above-described method, as is the case with the method(1), in forming a thin film, the entire surface of the substrate is notheated but only a portion of the substrate necessary for film formationis selectively heated, and thus a reduction in process temperature isachieved.

[0025] As for thin film deposition, in the case, for example, ofemploying chemical techniques such as CVD, film deposition needs to beperformed with the substrate surface having been set to a temperatureequal to or above a given temperature. For this reason, a region of thesubstrate not reaching the above-described temperature cannot obtain adeposition rate required for deposition on the substrate. Thus, when thesubstrate is selectively heated in the manner described in theabove-described method, only a region on the substrate having beenheated obtains a deposition rate required for film formation, andtherefore a thin film can be deposited only such a region. Consequently,a thin film with a predetermined pattern can be formed withoutperforming a lithography step conventionally required when patterning athin film, which in turn reduces the number of fabrication steps,resulting in a reduction in costs.

[0026] In the above-described methods (1) and (2), the substrate may beselectively heated by forming, on the substrate, an energy absorber oran energy absorber with a predetermined pattern, and subsequentlyimparting energy to the energy absorber to release heat from the energyabsorber. Here, the energy absorber refers to as a substance thatabsorbs thermal energy, electromagnetic energy, or the like and thenreleases such energy in the form of heat.

[0027] Furthermore, the energy may be imparted by irradiating anelectromagnetic wave to the energy absorber. An example of theelectromagnetic wave includes light.

[0028] Moreover, in the above-described methods (1) and (2), thesubstrate may be selectively heated by forming, on the substrate, aconductive film or a conductive film with a predetermined pattern, andsubsequently passing an electric current through the conductive film torelease heat from the conductive film.

[0029] In addition, it is preferable that the substrate be selectivelyheated intermittently. When the substrate is heated continuously for acertain period of time, the temperature difference between a region witha high temperature and a region with a low temperature on the substratesurface is made small, making it impossible to make a clear differencebetween the two different regions On the other hand, when the substrateis heated intermittently, because of the characteristics of the energyabsorber that releases absorbed energy as heat, the temperaturedifference between the two different regions can be made clearly. Thus,it is possible to clearly vary the film properties of a thin film to beformed on the substrate, obtaining a desired pattern, while preventingthe formation of an abnormal pattern.

[0030] Furthermore, in the step of forming the thin film according tothe above-described method (1) and in the step of depositing the thinfilm according to the above-described method (2), it is preferable toemploy CVD. Further, in the above-described method (1), among the CVDtechniques, it is more preferable to employ plasma enhanced CVD.

[0031] Methods of Fabricating a Thin Film Transistor)

[0032] (1) In order to overcome the foregoing problems, there isprovided a method of fabricating a thin film transistor according to thepresent invention comprising: forming, on an insulating substrate, ametal thin film with a predetermined pattern; forming an insulatinglayer on the metal thin film; forming a semiconductor thin film on theinsulating layer, the semiconductor thin film with film propertiesvarying between a region above and in the vicinity of the metal thinfilm and other regions being formed by imparting energy to the metalthin film to release the energy as heat from the metal thin film so thatthe insulating layer is selectively heated; and patterning thesemiconductor thin film in a predetermined pattern by etching thesemiconductor thin film to selectively remove the other regions.

[0033] With the above-described method, when forming a semiconductorthin film, only a portion of the insulating substrate necessary for filmformation is selectively heated, and thus a significant increase insubstrate temperature can be prevented, reducing the processtemperature. Consequently, it is also possible to form a thin filmtransistor, for example, on a flexible substrate.

[0034] In addition, with the above-described method, a semiconductorthin film with film properties varying from region to region can beformed, and thus even if etching is performed under the same conditions,only a specified portion can be selectively removed. Consequently, asemiconductor thin film with a predetermined pattern can be formedwithout using a mask, achieving a reduction in fabrication costs.

[0035] (2) Furthermore, in order to overcome the foregoing problems,there is provided another method of fabricating a thin film transistoraccording to the present invention comprising: forming, on an insulatingsubstrate, a metal thin film with a predetermined pattern; forming aninsulating layer on the metal thin film; and depositing a semiconductorthin film on the insulating layer, the semiconductor thin film beingdeposited only in a specified region by imparting energy to the metalthin film to release the energy as heat from the metal thin film so thatthe insulating layer is selectively heated, thereby varying a depositionrate from region to region on the insulating layer.

[0036] With the above-described method, as is the case with the method(1), in forming a semiconductor thin film, the entire surface of theinsulating substrate is not heated but only a portion of the substratenecessary for film formation is selectively heated, and thus a reductionin process temperature is achieved.

[0037] In addition, in the above-described method, the selective heatingof the insulating substrate allows to vary deposition conditions fromregion to region on the insulating substrate. Consequently, asemiconductor thin film can be deposited only in a desired region, andthus a semiconductor thin film with a predetermined pattern can beformed without performing a lithography step conventionally required.Thus, the number of fabrication steps is reduced, resulting in areduction in costs.

[0038] In the above-described methods (1) and (2), the metal thin filmmay serve as a gate electrode or a source electrode and a drainelectrode.

[0039] In addition, the insulating layer may be selectively heated byirradiating an electromagnetic wave, serving as the energy, to the metalthin film to release heat from the metal thin film.

[0040] In the above-described methods (1) and (2), the insulating layermay be selectively heated by passing an electric current through themetal thin film to release heat from the metal thin film.

[0041] Further, in the above-described methods (1) and (2), it ispreferable that the energy be imparted to the metal thin filmintermittently. When the substrate is heated continuously for a certainperiod of time, the temperature difference between a region with a hightemperature and a region with a low temperature on the substrate surfaceis made small, making it impossible to make a clear difference betweenthe two different regions. On the other hand, when the substrate isheated intermittently, the temperature difference between the twodifferent regions can be made clearly, and accordingly it is possible toclearly vary the film properties of a semiconductor thin film to beformed on the substrate. Consequently, a pattern of the semiconductorthin film obtained after etching can be made distinctly.

[0042] In the above-described methods (1) and (2), in the step offorming the thin film, it is preferable to employ CVD. Further, amongthe CVD techniques, it is more preferable to employ plasma enhanced CVD.

[0043] Moreover, in the above-described methods (1) and (2), after thestep of depositing the semiconductor thin film, the semiconductor thinfilm may be crystallized.

[0044] In addition, laser annealing may be performed instead of the heattreatment.

[0045] (3) Moreover, in order to overcome the foregoing problems, thereis provided still another method of fabricating a thin film transistoraccording to the present invention comprising: forming, on an insulatingsubstrate, a metal thin film with a predetermined pattern; forming afirst semiconductor thin film on the insulating substrate with theinsulating substrate being selectively heated by imparting energy to themetal thin film to release the energy as heat from the metal thin film,the first semiconductor thin film having film properties varying betweena portion covering the metal thin film and other portions; patterningthe first semiconductor thin film by etching the first semiconductorthin film to selectively remove only the other portions, therebycovering only the metal thin film; forming, on the insulating substratehaving the first semiconductor thin film thereon, a second semiconductorthin film with a higher melting point than the first semiconductor thinfilm; and crystallizing the second semiconductor thin film by heattreatment with the first semiconductor thin film as growth nucleus.

[0046] (4) In order to overcome the foregoing problems, there isprovided yet another method of fabricating a thin film transistoraccording to the present invention comprising: forming, on an insulatingsubstrate, a metal thin film with a predetermined pattern; depositing afirst semiconductor thin film so as to cover the metal thin film, thefirst semiconductor thin film being deposited only on top and sidesurfaces of the metal thin film, by imparting energy to the metal thinfilm to release the energy as heat from the metal thin film so that adeposition rate varies between a region in the vicinity of the metalthin film and other regions; forming, on the insulating substrate havingthe first semiconductor thin film thereon, a second semiconductor thinfilm with a higher melting point than the first semiconductor thin film;and crystallizing the second semiconductor thin film by heat treatmentwith the first semiconductor thin film as growth nucleus.

[0047] (5) In order to overcome the foregoing problems, there isprovided another method of fabricating a thin film transistor accordingto the present invention comprising: forming, on an insulatingsubstrate, a metal thin film with a predetermined pattern; forming aninsulating layer on the insulating substrate having the metal thin filmthereon; forming a first semiconductor thin film on the insulatinglayer, the first semiconductor thin film with film properties varyingfrom region to region on the insulating layer being formed by impartingenergy to the metal thin film to release the energy as heat from themetal thin film so that the insulating layer is selectively heated;patterning the first semiconductor thin film in a predetermined patternby etching the first semiconductor thin film to selectively remove onlya portion of the first semiconductor thin film with specified filmproperties; forming, on the insulating substrate having the firstsemiconductor thin film thereon, a second semiconductor thin film with ahigher melting point than the first semiconductor thin film; andcrystallizing the second semiconductor thin film by heat treatment withthe first semiconductor thin film as growth nucleus.

[0048] (6) In order to overcome the foregoing problems, there isprovided still another method of fabricating a thin film transistoraccording to the present invention comprising: forming, on an insulatingsubstrate, a metal thin film with a predetermined pattern; forming aninsulating layer on the insulating substrate having the metal thin filmthereon; depositing a first semiconductor thin film on the insulatinglayer, the first semiconductor thin film being deposited only in aspecified region by imparting energy to the metal thin film to releasethe energy as heat from the metal thin film so that the insulating layeris selectively heated, thereby varying a deposition rate from region toregion on the insulating layer; forming, on the insulating substratehaving the first semiconductor thin film thereon, a second semiconductorthin film with a higher melting point than the first semiconductor thinfilm; and crystallizing the second semiconductor thin film by heattreatment with the first semiconductor thin film as growth nucleus.

[0049] In the above-described methods (3) to (6), the metal thin filmmay serve as a gate electrode or a source electrode and a drainelectrode. Specifically, when the metal thin film serves as the gateelectrode, in the above-described methods, a bottom-gate type thin filmtransistor can be fabricated. On the other hand, when the metal thinfilm serves as the source electrode and the drain electrode, in theabove-described methods, a top-gate type thin film transistor can befabricated.

[0050] Furthermore, in the above-described methods (3) to (6), theinsulating layer may be selectively heated by irradiating anelectromagnetic wave, serving as the energy, to the metal thin film torelease heat from the metal thin film.

[0051] In the above-described methods (3) to (6), the insulating layermay be selectively heated by passing an electric current through themetal thin film to release heat from the metal thin film.

[0052] In the above-described methods (3) to (6), it is preferable thatthe energy be imparted to the metal thin film intermittently.

[0053] In the above-described methods (3) to (6), in the step of formingthe thin film, it is preferable to employ CVD. Further, among the CVDtechniques, it is more preferable to employ plasma enhanced CVD.

[0054] In the above-described methods (3) to (6), after the step offorming the semiconductor thin film, the semiconductor thin film may becrystallized.

[0055] (Apparatus for Fabricating a Thin Film)

[0056] (1) In order to overcome the foregoing problems, there isprovided an apparatus for fabricating a thin film according to thepresent invention comprising: a metal thin film formation means forforming, on a substrate, a metal thin film with a predetermined pattern;a thin film formation means for forming a thin film on the substrate,the thin film with film properties varying from region to region on thesubstrate being formed by imparting energy to the metal thin film torelease the energy as heat from the metal thin film so that thesubstrate is selectively heated; and an etching means for patterning thethin film in a predetermined pattern by etching the thin film toselectively remove only a portion of the thin film with specified filmproperties.

[0057] (2) In addition, in order to overcome the foregoing problems,there is provided another apparatus for fabricating a thin filmaccording to the present invention comprising: a metal thin filmformation means for forming, on a substrate, a metal thin film with apredetermined pattern; and a thin film formation means for forming athin film on the substrate, the thin film being formed only in aspecified region by imparting energy to the metal thin film to releasethe energy as heat from the metal thin film so that the substrate isselectively heated, thereby varying a deposition rate from region toregion on the substrate.

[0058] In the above-described configurations (1) and (2), the thin filmformation means may comprise: a reaction vessel for holding thesubstrate inside; an electromagnetic wave irradiation portion forirradiating an electromagnetic wave, serving as the energy, to the metalthin film; a supply portion for supplying a source gas to an inside ofthe reaction vessel; and a reaction excitation portion for exciting achemical reaction of the source gas.

[0059] (Thin Film Transistors)

[0060] (1) In order to overcome the foregoing problems, there isprovided a thin film transistor according to the present inventioncomprising: a metal thin film having a predetermined pattern andprovided on an insulating substrate; an insulating layer provided on theinsulating substrate having the metal thin film thereon; and asemiconductor thin film having a predetermined pattern and provided onthe insulating layer, wherein the semiconductor thin film is patternedin the predetermined pattern by forming the semiconductor thin film byimparting energy to the metal thin film to release the energy as heatfrom the metal thin film so that the insulating layer is selectivelyheated, thereby varying film properties between a region above and inthe vicinity of the metal thin film and other regions, and subsequentlyetching the semiconductor thin film to selectively remove the otherregions.

[0061] (2) In addition, in order to overcome the foregoing problems,there is provided another thin film transistor according to the presentinvention comprising: a metal thin film having a predetermined patternand provided on an insulating substrate; an insulating layer provided onthe insulating substrate having the metal thin film thereon; and asemiconductor thin film having a predetermined pattern and provided onthe insulating layer, wherein the semiconductor thin film is depositedonly in a specified region by imparting energy to the metal thin film torelease the energy as heat from the metal thin film so that theinsulating layer is selectively heated, thereby varying a depositionrate from region to region on the insulating layer.

[0062] Furthermore, in the above-described methods (1) and (2), asidewall of the semiconductor thin film may have a gently sloping shape.With conventional etching, the sidewall is perpendicular to thesubstrate surface and there is much of a step height between thesemiconductor thin film and the insulating layer. Thus, when, forexample, a source electrode, a drain electrode, and the like are formedon the semiconductor thin film, disconnection may occur due to the stepheight. However, as in the above-described configurations, when thesidewall of the semiconductor thin film has a gently sloping shape, itis possible to minimize occurrence of disconnection.

[0063] (3) In order to overcome the foregoing problems, there isprovided still another thin film transistor according to the presentinvention comprising: a metal thin film patterned on an insulatingsubstrate in a predetermined pattern; a first semiconductor thin filmdeposited so as to cover the metal thin film, the first semiconductorthin film being provided so as to cover only the metal thin film, byimparting energy to the metal thin film to release the energy as heatfrom the metal thin film, thereby providing the first semiconductor thinfilm with film properties varying between a portion covering the metalthin film and other regions, and subsequently selectively removing theother portions by etching; and a second semiconductor thin film providedon the insulating substrate having the first semiconductor thin filmthereon, and having a higher melting point than the first semiconductorthin film, the second semiconductor thin film being crystallized by heattreatment with the first semiconductor thin film as growth nucleus,wherein a region of the crystallized second semiconductor thin film nothaving the first semiconductor thin film serves as a channel portion.

[0064] (4) Moreover, in order to overcome the foregoing problems, thereis provided yet another thin film transistor according to the presentinvention comprising: a metal thin film patterned on an insulatingsubstrate in a predetermined pattern; a first semiconductor thin filmdeposited so as to cover the metal thin film, the first semiconductorthin film being deposited on top and side surfaces of the metal thinfilm, by imparting energy to the metal thin film to release the energyas heat from the metal thin film so that a deposition rate variesbetween a region in the vicinity of the metal thin film and otherregions; a second semiconductor thin film provided on the insulatingsubstrate having the first semiconductor thin film thereon, and having ahigher melting point than the first semiconductor thin film, the secondsemiconductor thin film being crystallized by heat treatment with thefirst semiconductor thin film as growth nucleus, wherein a region of thecrystallized second semiconductor thin film not having the firstsemiconductor thin film serves as a channel portion.

[0065] Furthermore, in order to overcome the foregoing problems, thereis provided another thin film transistor according to the presentinvention comprising: a metal thin film patterned on an insulatingsubstrate in a predetermined pattern; an insulating layer provided onthe insulating substrate having the metal thin film thereon; a firstsemiconductor thin film formed on the insulating layer with theinsulating layer being selectively heated by imparting energy to themetal thin film to release the energy as heat from the metal thin film,thereby varying film properties of the first semiconductor thin filmbetween a portion corresponding to a region with a high surfacetemperature of the insulating layer and a portion corresponding to aregion with a low surface temperature of the insulating layer, the firstsemiconductor thin film being provided only in the region with a highsurface temperature, by etching the first semiconductor thin film toselectively remove the portion corresponding to the region with a lowsurface temperature; and a second semiconductor thin film provided onthe insulating substrate having the first semiconductor thin filmthereon, and having a higher melting point than the first semiconductorthin film, the second semiconductor thin film being crystallized by heattreatment with the first semiconductor thin film as growth nucleus,wherein a region of the crystallized second semiconductor thin film nothaving the first semiconductor thin film serves as a channel portion.

[0066] In order to overcome the foregoing problems, there is providedstill another thin film transistor according to the present inventioncomprising: a metal thin film patterned on an insulating substrate in apredetermined pattern; an insulating layer provided on the insulatingsubstrate having the metal thin film thereon; a first semiconductor thinfilm provided on the insulating layer, the insulating layer selectivelyheated by imparting energy to the metal thin film to release the energyas heat from the metal thin film so that a deposition rate variesbetween a region with a high surface temperature of the insulating layerand a region with a low surface temperature of the insulating layer,thereby providing the first semiconductor thin film only in the regionwith a high surface temperature; and a second semiconductor thin filmprovided on the insulating substrate having the first semiconductor thinfilm thereon, and having a higher melting point than the firstsemiconductor thin film, the second semiconductor thin film beingcrystallized by heat treatment with the first semiconductor thin film asgrowth nucleus, wherein a region of the crystallized secondsemiconductor thin film not having the first semiconductor thin filmserves as a channel portion.

BRIEF DESCRIPTION OF THE DRAWINGS

[0067]FIG. 1 is a cross-sectional view showing the fabrication step of athin film according to Embodiment 1 of the present invention andillustrating the situation in which a surface of an insulating layer isselectively heated.

[0068]FIG. 2 is a cross-sectional view showing the fabrication step ofthe thin film according to Embodiment 1 and illustrating the situationin which a semiconductor thin film has been formed on the insulatinglayer.

[0069] FIGS. 3(a) and (b) are diagrams for illustrating selectiveheating of a substrate, in a method of fabricating a thin film accordingto Embodiment 1. FIG. 3(a) is a graph showing temperature distributionson the surface of the insulating layer, and FIG. 3(b) is across-sectional view showing the main part of the substrate.

[0070]FIG. 4 is a graph showing the relationship between irradiationenergy and irradiation time of light, in the method of fabricating athin film according to Embodiment 1.

[0071]FIG. 5 is a graph showing the relationship between SiH₂/SiH ratioor etching rate and temperature on the surface of the insulating layer,in the method of fabricating a thin film according to Embodiment 1.

[0072]FIG. 6 is a cross-sectional view for illustrating etching of thesemiconductor thin film, in the method of fabricating a thin filmaccording to Embodiment 1.

[0073]FIG. 7 is a cross-sectional view showing the semiconductor thinfilm fabricated by the method of fabricating a thin film according toEmbodiment 1.

[0074]FIG. 8 is a graph showing the relationship between deposition rateand temperature on a surface of an insulating layer, in a method offabricating a thin film according to Embodiment 2 of the presentinvention.

[0075]FIG. 9 is a cross-sectional view for illustrating a method offabricating a thin film according to Embodiment 3 of the presentinvention.

[0076] FIGS. 10(a) and 10(b) are diagrams for illustrating selectiveheating of a substrate, in the method of fabricating a thin filmaccording to Embodiment 3. FIG. 10(a) is a graph showing temperaturedistributions on a surface of an insulating layer, and FIG. 10(b) is across-sectional view showing the main part of the substrate.

[0077]FIG. 11 is a graph showing the relationship between the amount ofelectrical current and application time, in the method of fabricating athin film according to Embodiment 3.

[0078]FIG. 12 is a cross-sectional view for illustrating etching of asemiconductor thin film, in the method of fabricating a thin filmaccording to Embodiment 3.

[0079] FIGS. 13(a) and 13(b) are cross-sectional views showing thefabrication steps of a semiconductor thin film according to Embodiment 5of the present invention. FIG. 13(a) is a cross-sectional view forillustrating the formation of first and second semiconductor thin films,and FIG. 13(b) is a cross-sectional view for illustrating thecrystallization of the second semiconductor thin film.

[0080] FIGS. 14(a) and 14(b) are cross-sectional views showing thefabrication steps of a semiconductor thin film according to Embodiment 6of the present invention. FIG. 14(a) is a cross-sectional view forillustrating the formation of first and second semiconductor thin films,and FIG. 14(b) is a cross-sectional view for illustrating thecrystallization of the second semiconductor thin film.

[0081]FIG. 15 is a plan view schematically showing an apparatus forfabricating a thin film transistor used in Example 1 of the presentinvention.

[0082]FIG. 16 is a cross-sectional view schematically showing a plasmaenhanced CVD system used in Example 1 of the present invention.

[0083] FIGS. 17(a) to 17(e) are cross-sectional views for illustratingthe fabrication steps of a thin film transistor according to Example 1of the present invention.

[0084] FIGS. 18(a) to 18(c) are cross-sectional views for illustratingthe fabrication steps of a thin film transistor according to Example 2of the present invention.

[0085] FIGS. 19(a) to 19(d) are cross-sectional views for illustratingthe fabrication steps of a thin film transistor according to Example 9of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0086] In the present invention, a thin film is formed with thesubstrate having a temperature distribution, thereby reducing theprocess temperature and enabling the formation of a thin film having apredetermined pattern without performing a lithography step using amask.

[0087] A more specific description is as follows.

[0088] (1) The substrate surface is selectively heated to form a thinfilm with film properties varying from region to region. By takingadvantage of differences in the etching rate caused by this variation infilm properties, it is possible to perform patterning without performinga lithography step using a mask.

[0089] (2) The substrate surface is selectively heated so that thedeposition rate itself varies from region to region. By taking advantageof differences in the deposition rate, a thin film is formed only inspecific regions on the substrate without performing a lithography step.

[0090] Embodiment 1

[0091] Embodiment 1 corresponds to the case (1) described above. As ameans for selectively heating the substrate surface, an energy absorberis utilized, making it possible to form a thin film with film propertiesvarying from region to region.

[0092] The energy absorber according to the present embodiment functionssuch that when the energy absorber is irradiated with electromagneticwaves such as light, the energy absorber absorbs the electromagneticwaves as energy and further releases the energy as heat. An energyabsorber having such a function can be formed, for example, of highmelting point metals such as Mo, Ti, Cu, and Au.

[0093] The energy absorber is formed as follows. Specifically, as shownin FIG. 1, on a substrate 1, being a glass substrate, a precursor filmof energy absorbers 2 is formed by sputtering or the like, and then thefilm is patterned in a predetermined pattern to form the energyabsorbers 2. For the patterning, photolithography, for example, can beemployed.

[0094] Next, on the substrate 1 provided with the energy absorbers 2, aninsulating layer 3 such as SiO₂ or Si_(x) is formed.

[0095] Furthermore, as shown in FIG. 2, with the substrate 1 beingheated, a semiconductor thin film 6 made of an a-Si thin film is formedon the insulating layer 3 by, for example, plasma enhanced CVD.

[0096] The heating of the substrate 1 is carried out, for example, asfollows. Specifically, light 4 is irradiated onto the entire surface ofthe substrate 1 from the other side of the deposited surface of thesubstrate 1. As an energy source utilized for light irradiation, forexample, a halogen lamp, a xenon lamp, or a metal halide lamp isutilized.

[0097] When the light 4 is irradiated onto the substrate 1, the energyabsorbers 2 absorb the light 4 as light energy, and then release thelight energy as heat. Thus, regions in the vicinity of the energyabsorbers 2 have a higher temperature than other regions where theenergy absorbers 2 are not provided. When this state is observed as thebasis for the substrate temperature, roughly, such a temperaturedistribution as to be shown by the dotted line in FIG. 3(a) is obtained.FIG. 3(a) is a graph showing temperature distributions at the main partof the substrate 1 shown in FIG. 3(b) and showing the relationshipbetween the length (μm) of the cross section of the substrate 1 andsubstrate temperature (° C.). As can be seen from FIG. 3(a), when thesubstrate temperature in regions where the energy absorbers 2 arepresent is set, for example, to about 300° C., the substrate temperatureat locations, a few pm away from the energy absorbers 2 is about 200° C.

[0098] The reason for setting the substrate temperature in regions wherethe energy absorbers 2 are present to about 300° C. is related to thedeposition process of the semiconductor thin film 6 made of an a-Si thinfilm. Specifically, in the case where the semiconductor thin film 6 isformed by, for example, plasma enhanced CVD, the deposition temperatureneeds to be set to about 300° C. Thus, the above-mentioned substratetemperature is only an exemplifying value, and therefore the substratetemperature should be changed and set in accordance with materials anddeposition methods for a thin film to be formed. Note that the substratetemperature specifically means the surface temperature of the insulatinglayer 3. However, in the present invention, it is also possible todeposit a semiconductor thin film directly on the energy absorbers 2without providing the insulating layer 3. In such a case, the substratetemperature means the surface temperature of the substrate 1 (thesubstrate temperature in regions where the energy absorbers 2 arepresent is the surface temperature of the energy absorbers 2).

[0099] Methods of irradiating light onto the substrate 1 are notparticularly limited; however, for example, as is shown in FIG. 4showing the relationship between irradiation energy (J) and irradiationtime (sec) of light, it is preferable to irradiate light intermittentlyat specified intervals. In doing so, it is possible to prevent thetemperature distribution of the substrate 1 from making a smoothdistribution curve, as shown by the dot-dash line in FIG. 3(a).Intermittent light irradiation can be performed by, for example,controlling the ON and OFF of the power source of the energy source.

[0100] With the surface of the substrate 1 thus having a temperaturedistribution, the semiconductor thin film 6 made of an a-Si thin film isformed on the insulating layer 3 by plasma enhanced CVD. As a flux 5necessary for forming the semiconductor thin film 6, SiH₄ gas isutilized. When the SiH₄ is utilized, the SiH₄ is decomposed by theplasma and radicals of SiH_(x) (X=0, 1, 2, 3) are generated. As aresult, an a-Si thin film is formed. The supply of flux for depositionis made possible with such an equipment system that is capable ofsupplying a flux using a device configuration such as plasma enhancedCVD.

[0101] The film properties of the semiconductor thin film 6 deposited onthe substrate 1 greatly depend on the power, operating pressure, gasflow rate, substrate temperature, and the like of plasma enhanced CVD.By optimizing the conditions of the power of plasma enhanced CVD and thesupply of SiH₄ gas, it is possible to deposit, on the substrate 1 with asubstrate temperature of 300° C., an a-Si thin film with excellent filmproperties, containing therein few SiH₂ bonds.

[0102] The variation of the film properties of an a-Si thin film wasexamined in the case, for example, where the substrate temperature wasvaried under the same plasma conditions, and as a result, a curve shownby the solid line in FIG. 5 was obtained. FIG. 5 is a graph showing therelationship between SiH₂/SiH ratio or etching rate (nm/sec) andsubstrate temperature (° C.). As can be seen from the graph, as thesubstrate temperature decreases, the SiH₂/SiH ratio increases. Inaddition, the graph shows that when the substrate temperature is 300°C., the SiH₂/SiH ratio is lowest. These results show that the a-Si filmcontains few SiH₂ bonds therein.

[0103] Thus, in the semiconductor thin film 6 formed on the insulatinglayer 3, the film properties vary between regions 6 a formed on theenergy absorbers 2 and regions 6 b other than the regions 6 a.Specifically, in the regions 6 a, since the substrate temperature wasabout 300° C., the film in such regions contained few SiH₂ bonds andthus had film properties with many SiH bonds. On the contrary, in theregions 6 b, the substrate temperature was about 200° C., and thus thefilm in such regions had film properties with numerous SiH₂ bonds.

[0104] Next, the semiconductor thin film 6 is etched without performinga lithography step (see FIG. 6). As described above, the semiconductorthin film 6 is a thin film such that the film properties vary betweenthe regions 6 a and the regions 6 b. This variation in film propertiesappears as differences in the etching rate upon etching. Therelationship between the variation in film properties and etching ratecan be clearly seen from the test results, as will be described below.Specifically, the etching rate for a-Si thin films deposited withdifferent substrate temperatures was measured, and as a result, a curveshown by the dotted line in FIG. 5 was obtained. The measured values areobtained by hydrogen plasma treatment. As is clear from this graph, theetching rate upon etching of the semiconductor thin film 6 is higher inthe regions 6 b than in the regions 6 a. Thus, even if etching isperformed in the regions 6 a and the regions 6 b under the sameconditions, the film properties vary between the two different regions,causing differences in the etching rate. Consequently, only the portionsof the regions 6 b are selectively removed, and thus a semiconductorthin film 6 with a predetermined pattern, as shown in FIG. 7, can beformed. Here, sidewall portions 8 of removed etching portions 7 have agently sloping taper shape. Note that although the results shown in FIG.5 were obtained by hydrogen plasma treatment, even in the case of plasmatreatment such as CF₄, differences in the etching rate were broughtabout.

[0105] According to the method of fabricating a thin film of the presentembodiment described above, a semiconductor thin film with apredetermined pattern can be formed at low temperatures, which in turnallows a thin film to be formed easily on a flexible substrate, forexample. In addition, it is not necessary to perform a lithography stepconventionally required when patterning a thin film, and thus the numberof fabrication steps is reduced, resulting in a reduction in costs.Moreover, since an a-Si thin film formed in the present embodimentcontains few SiH₂ bonds, when such an a-Si thin film is applied to athin film transistor, the thin film transistor with high mobility andhigh quality can be obtained. Furthermore, the a-Si thin film has fewdefects therein, achieving a reduction in leakage current in an OFFstate.

[0106] Embodiment 2

[0107] Embodiment 2 corresponds to the case (2) described above. Thepresent embodiment and the foregoing Embodiment 1 are the same in thatboth embodiments employ an energy absorber as a means for selectivelyheating the substrate surface. However, the present embodiment isdifferent from the foregoing Embodiment 1 in that the substrate surfaceis selectively heated so that the deposition rate itself varies fromregion to region on the substrate, thereby forming a thin film only inspecific regions.

[0108] In order that the deposition rate varies from region to region onthe substrate, in the present embodiment, the substrate temperature in aregion in the vicinity of the surface of an energy absorber 2 was set toabout 400° C., as is shown by the solid line in FIG. 3. Here, thesubstrate temperature at a location, a few um away from the energyabsorber, was about 300° C. The reason for setting the temperature ofthe surface of the energy absorber 2 to about 400° C. is that whendepositing a semiconductor thin film by low-pressure CVD using Si₂H₆,the temperature needs to be set to a level at which the Si₂H₆ isthermally decomposed (i.e., 400° C.) Thus, the above-mentioned substratetemperature is only an exemplifying value, and therefore the substratetemperature should be changed and set in accordance with materials anddeposition methods for a thin film to be formed.

[0109] A semiconductor thin film is formed as follows. As is the caseabove, with the surface of a substrate 1 having a temperaturedistribution, a semiconductor thin film made of an a-Si thin film isformed on an insulating layer by low-pressure CVD. As a flux necessaryfor forming the semiconductor thin film, the above-mentioned Si₂H₆ isutilized. As for deposition conditions, as is the case above, thesubstrate temperature is set to 400° C., and in addition, for example,the operating pressure and gas flow rate of low-pressure CVD are set toabout 300 mTorr and about 100 sccm, respectively. In the case wherelow-pressure CVD is not employed, it is also possible to form asemiconductor thin film by thermal CVD.

[0110] At this point, on the substrate 1, there are formed regions wherethe a-Si thin film is deposited and regions where the a-Si thin film isnot deposited. Specifically, while the a-Si thin film is deposited inregions above and in the vicinity of energy absorbers 2, the a-Si thinfilm is not deposited in other regions. This can be explained, forexample, by the change in deposition rate in accordance with thesubstrate temperature, which is shown in FIG. 8. That is, in order thatthe thermal decomposition of Si₂H₆ takes place in the formation of afilm by low-pressure CVD, a temperature of, at least, about 400° C. isrequired. If the temperature is lower than this level, as is dear fromFIG. 8, the deposition rate is rapidly reduced, and when the substratetemperature is about 300° C., it is almost impossible to deposit an a-Sithin film.

[0111] According to the method of fabricating a thin film of the presentembodiment described above, a thin film with a predetermined pattern canbe formed without performing a lithography step conventionally requiredwhen patterning a thin film. Consequently, the number of fabricationsteps is reduced, resulting in a reduction in costs. In addition, ana-Si thin film formed in the present embodiment contains, as is theforegoing embodiment 1, few SiH₂ bonds, and thus when such an a-Si thinfilm is applied to a thin film transistor, the thin film transistor withhigh mobility and high quality can be obtained. Moreover, the a-Si thinfilm has few defects therein, achieving a reduction in leakage currentin an OFF state.

[0112] Note that the present embodiment described the case where Si₂H₆is used as a source gas; however, the present invention is not limitedthereto. For example, it is also possible to use SiH₄ gas. In such acase, the surface temperature of the energy absorbers 2 needs to be setto 550° C.

[0113] Embodiment 3

[0114] A method of fabricating a thin film according to Embodiment 3 isdifferent from a method of fabricating a thin film according to theforegoing Embodiment 1 in that a conductive film is utilized in place ofan energy absorber and an electric current is passed through theconductive film to selectively heat the substrate surface.

[0115] As is shown in FIG. 9, a conductive film is formed on a substrate1 and then pattered by any known method to form conductive films 9.

[0116] Next, on the substrate 1 provided with the conductive films 9, aninsulating layer 3 of SiO₂, SiN_(x), or the like is formed.

[0117] Further, as is shown in FIG. 9, with the substrate 1 beingheated, a semiconductor thin film 6 made of an a-Si thin film is formedon the insulating layer 3 by, for example, plasma enhanced CVD.

[0118] The heating of the substrate 1 is carried out as follows.Specifically, an electric current application portion 10 is connected tothe conductive films 9 so as to pass an electric current through theconductive films from the electric current application portion 10. Whenan electric current is passed through the conductive films 9, theconductive films 9 release electrical energy as heat. Thus, regions inthe vicinity of the conductive films 9 have a higher temperature thanother regions where the conductive films 9 are not provided. When thisstate is observed as the basis for the substrate temperature, roughly,such a temperature distribution as to be shown by the dotted line inFIG. 10(a) is obtained. The substrate temperature in regions where theconductive films 9 are present is set, as is the foregoing Embodiment 1,to about 300° C.

[0119] Furthermore, the electric current to be applied to the conductivefilms 9 is applied preferably in a pulsed fashion (intermittently), asis shown in FIG. 11 showing the relationship between the amount ofelectrical current and application time (sec).

[0120] With the surface of the substrate 1 thus having a temperaturedistribution, a semiconductor thin film 6 made of an a-Si thin film isformed, in the same manner as the foregoing Embodiment 1, on theinsulating layer 3 by plasma enhanced CVD. Thereafter, the semiconductorthin film was etched without performing a lithography step.Consequently, as is the case with the foregoing Embodiment 1, asemiconductor thin film with a predetermined pattern can be formed atlow temperatures (see FIG. 12). In addition, since it is not necessaryto perform a lithography step conventionally required when patterning athin film, the number of fabrication steps is reduced, resulting in areduction in costs. Moreover, when an a-Si thin film formed by a methodof fabricating a thin film according to the present embodiment isapplied to a thin film transistor, the thin film transistor, as is thecase with the foregoing Embodiment 1, which has high mobility and highquality and achieves a reduction in leakage current in an OFF state, canbe obtained.

[0121] Embodiment 4

[0122] A method of fabricating a thin film according to Embodiment 4 isdifferent from a method of fabricating a thin film according to theforegoing Embodiment 2 in that a conductive film is utilized in place ofan energy absorber and an electric current is passed through theconductive film to selectively heat the substrate surface.

[0123] First, in the same manner as the foregoing Embodiment 3, aconductive film is formed on a substrate by sputtering, and thenpatterned by any known method to form conductive films 9.

[0124] Next, on the substrate provided with the conductive films, aninsulating layer of SiO₂, SiN_(x), or the like is formed.

[0125] Further,with the substrate being heated, a semiconductor thinfilm made of an a-Si thin film is formed on the insulating layer by, forexample, plasma enhanced CVD.

[0126] The heating of the substrate is carried out as follows.Specifically, an electric current application portion is connected tothe conductive films so as to pass an electric current through theconductive films. When an electric current is passed through theconductive films, the conductive films release electrical energy asheat. Thus, regions in the vicinity of the conductive films have ahigher temperature than other regions where the conductive films are notprovided. When this temperature distribution is observed as the basisfor the substrate temperature, roughly, such a temperature distributionas to be shown by the solid line in FIG. 10(a) is obtained. Thesubstrate temperature in regions where the conductive films are presentis set, as is the foregoing Embodiment 1, to about 300° C.

[0127] Furthermore, the electric current to be applied to the conductivefilms is applied preferably in a pulsed fashion (intermittently), as isthe foregoing Embodiment 3 (see FIG. 11).

[0128] With the surface of the substrate thus having a temperaturedistribution, a semiconductor thin film made of an a-Si thin film isformed, in the same manner as the foregoing Embodiment 2, on theinsulating layer by low-pressure CVD. Consequently, as is the case withthe foregoing Embodiment 2, the a-Si thin film is deposited only inregions above and in the vicinity of the conductive films, and thus asemiconductor thin film with a predetermined pattern was formed.

[0129] As described above, according to a method of fabricating a thinfilm of the present embodiment, it is not necessary to perform alithography step conventionally required when patterning a thin film,and thus the number of fabrication steps is reduced, resulting in areduction in costs. Moreover, when an a-Si thin film formed by a methodof fabricating a thin film according to the present embodiment isapplied to a thin film transistor, the thin film transistor, as is thecase with the foregoing Embodiment 1, which has high mobility and highquality and achieves a reduction in leakage current in an OFF state, canbe obtained.

[0130] Embodiment 5

[0131] Embodiment 5 of the present invention is described below. FIGS.13(a) and 13(b) are cross-sectional views showing the fabrication stepsof a semiconductor thin film according to the present embodiment.

[0132] First, on a substrate 1, a precursor film of energy absorbers 21is formed by sputtering or the like, and then the film is patterned in apredetermined pattern to form the energy absorbers 21. The energyabsorbers 21 have basically the same function as energy absorbersdescribed in the foregoing Embodiment 1. In addition, the energyabsorbers 21 according to the present embodiment are made, for example,of any one type of metal selected from the group consisting of Ni, Pd,Pt, Ag, and Al, or of an alloy containing two or more types of metalselected from the same group.

[0133] A pattern is not particularly limited, and thus it is possible toform a plurality of the energy absorbers 21 in, for example, a dot orstripe pattern with an arbitrary space therebetween. In addition, for apatterning method, photolithography, for example, can be employed.

[0134] Next, after the energy absorbers 21 have been patterned, light isirradiated intermittently onto the entire surface of the substrate 1from the other side of the deposited surface of the substrate 1, so asto heat the substrate such that the substrate temperature in regions inthe vicinity of the surfaces of the energy absorbers 21 is about 400° C.In this state, first semiconductor thin films 22 are formed bylow-pressure CVD. At this point, the surfaces of the energy absorbers 2have a higher temperature than regions on the substrate 1 where theenergy absorbers 21 are not provided. Thus, the surfaces of the energyabsorbers 21 have a higher deposition rate than regions on the substratewhere the energy absorbers are not provided, making it possible to formthe first semiconductor thin films 22 only on the surfaces of the energyabsorbers 21. Here, examples of the first semiconductor thin film 22include an a-Ge film and an a-SiGe film. In addition, examples of a fluxused in thermal CVD for forming such films include GeH₄ gas and Si₂H₆gas. Furthermore, the film thickness of the first semiconductor thinfilm 22 should be in the range from about 10 to 50 nm.

[0135] Subsequently, on the substrate 1 and on the first semiconductorthin films 22, a second semiconductor thin film 23 made, for example, ofan a-Si thin film is formed. The second semiconductor thin film 23 canbe deposited by, for example, plasma enhanced CVD or low-pressure CVD.Moreover, the film thickness of the second semiconductor thin film 23should be in the range from about 30 to 100 nm.

[0136] Next, as is shown in FIG. 13(b), the second semiconductor thinfilm 23 is heat treated and crystallized. The crystallization firstbegins at the first semiconductor thin films 22 as the initial growthnucleus. Further, by the effect that the first semiconductor thin films22 are the starting point of solid phase growth, crystal growth in thelateral direction (lateral growth) occurs. Thereby, single crystalregions 24 with a grain size of about 2 to 3 μm are created in thevicinity of the first semiconductor thin films 22 being the center ofthe regions. Regions other than the single crystal regions 24 remain inan amorphous state. The first semiconductor thin films 22 become theinitial growth nucleus because the first semiconductor thin films 22have a lower melting point than the second semiconductor thin film 23.In addition, the energy absorbers 21 serve as a catalyst for reducingthe potential barrier so as to crystallize the second semiconductor thinfilm 23. Here, the second semiconductor thin film 23 is a semiconductorthin film preferably with a higher melting point than the firstsemiconductor thin films 22. This is because when crystallizing thesecond semiconductor thin film 23, by allowing crystallization to firstbegin at the first semiconductor thin films 22 with a low melting point,the first semiconductor thin films 22 can function as the initial growthnucleus. Further, the second semiconductor thin film 23 is preferablymade of a material different from a material for the first semiconductorthin films 22. This is because when a metal film made of theabove-described metal is utilized for the energy absorbers 21, diffusionof the above-described metal into the second semiconductor thin film 23caused by heat treatment performed for crystallizing the secondsemiconductor thin film 23 can be prevented. Moreover, in view of theprevention of diffusion, it is preferable that a film made of an alloybe used for the energy absorbers 21. Note that for heat treatmentconditions, for example, the treatment temperature can be set to to 600°C. and the treatment time can be set to 3 hours or more.

[0137] The second semiconductor thin film 23 can also be crystallized byintermittently irradiating excimer laser to the energy absorbers 21 andregions in the vicinity of the energy absorbers 21, instead ofperforming the above-described heat treatment. In this case, theirradiated first semiconductor thin films 22 melt to the liquid phaseonce, and as liquid-phase regions expand around the semiconductor thinfilms in the lateral direction, crystallization proceeds. Thereby, thesingle crystal regions 24 are formed in which the crystals have beengrown to about 4 to 5 μm in size. In the cooling process afterirradiation, solidification proceeds within the range of laser shotirradiation (i.e., the single crystal regions 24), from the outer to theinner.

[0138] The single crystal region 24 thus obtained is a very highperformance thin film. When the single crystal region 24 is applied, forexample, to the channel portion of a TFT, the TFT with high mobility canbe obtained. Such a TFT can be applied not only to an active matrixliquid crystal display capable of realizing a high definition display,but also to a built-in drive circuit in which high-speed operation isdemanded. In addition, such a TFT can be applied to an organic EL devicein which a TFT for current drive is required in the pixel portion

[0139] Note that the present embodiment described an example thatapplied a method of fabricating a thin film according to the foregoingEmbodiment 2; however, the present invention is not limited thereto. Itis also possible to apply a method of fabricating a thin film accordingto the foregoing Embodiment 2.

[0140] Embodiment 6

[0141] Embodiment 6 of the present invention is described below.

[0142] FIGS. 14(a) and 14(b) are cross-sectional views showing thefabrication steps of a semiconductor thin film according to the presentembodiment.

[0143] First, in the same manner as the foregoing Embodiment 5, on asubstrate 1, energy absorbers 21 with a predetermined pattern areformed. Then, an insulating layer 26 is formed by plasma enhanced CVD.

[0144] Subsequently, light is irradiated intermittently onto the entiresurface of the substrate 1 from the other side of the deposited surfaceof the substrate 1 to heat the substrate such that the substratetemperature in regions in the vicinity of the surfaces of the energyabsorbers 21 is about 400° C. In this state, first semiconductor thinfilms 22 are formed by low-pressure CVD. At this point, regions aboveand in the vicinity of the energy absorbers 21 in the insulating layer26 have a higher temperature than other regions. Thus, the firstsemiconductor thin films 27 are formed only on the surfaces of theenergy absorbers 21. Here, examples of the first semiconductor thin film27 include an a-Ge film and an a-SiGe film. In addition, examples of aflux used in thermal CVD for forming such films include GeH₄ gas andSi₂H₆ gas. Furthermore, the film thickness of the first semiconductorthin film 27 should be in the range from about 10 to 50 nm.

[0145] Subsequently, on the substrate 1 and the first semiconductor thinfilms 27, a second semiconductor thin film 28 made, for example, of ana-Si thin film is formed. The second semiconductor thin film 28 can bedeposited by, for example, plasma enhanced CVD or low-pressure CVD.Moreover, the film thickness of the second semiconductor thin film 28should be in the range from about 30 to 100 nm.

[0146] Moreover, as is shown in FIG. 14(b), the second semiconductorthin film 28 is irradiated with excimer laser 25 and crystallized. Thecrystallization begins, as is the foregoing Embodiment 5, at the firstsemiconductor thin films 27 as the initial growth nucleus, and lateralgrowth occurs on the first semiconductor thin films 27 as the startingpoint of solid phase growth. Further, in the cooling process afterirradiation, solidification proceeds within the range of laser shotirradiation (i.e., the single crystal regions 29), from the outer to theinner. As a result, as is the foregoing Embodiment 5, single crystalregions 29 with a grain size of about 4 to 5 μm can be formed in thesecond semiconductor thin film 28. Note that regions other than thesingle crystal regions 29 remain in an amorphous state.

[0147] The single crystal region 29 thus obtained is a very highperformance thin film. When such a region is applied, for example, tothe channel portion of a TFT, the TFT with high mobility can beobtained. Hence, it is possible to provide a TFT applicable to an activematrix liquid crystal display capable of realizing a high definitiondisplay and a TFT suitable for built-in drive circuit in whichhigh-speed operation is demanded. In addition, such a TFT can be appliedto an organic EL device in which a TFT for current drive is required inthe pixel portion.

[0148] Note that the present embodiment described an example thatapplied a method of fabricating a thin film according to the foregoingEmbodiment 2; however, the present invention is not limited thereto. Itis also possible to apply a method of fabricating a thin film accordingto the foregoing Embodiment 2.

[0149] The present invention is described in more detail below withreference to the examples; however, the present invention is not limitedthereto.

EXAMPLE 1

[0150] Example 1 is such that a method of fabricating a thin filmaccording to the foregoing Embodiment 1 is applied to the fabrication ofa thin film transistor. FIG. 15 is a plan view schematically showing anapparatus for fabricating a thin film transistor used in Example 1. FIG.16 is a cross-sectional view schematically showing a plasma enhanced CVDsystem used in Example 1. FIGS. 17(a) to 17(e) are cross-sectional viewsfor illustrating the fabrication steps of a thin film transistoraccording to Example 1.

[0151] First, an apparatus for fabricating a thin film transistor usedin Example 1 is described. This fabrication apparatus has, as shown inFIG. 15, a multi-chamber configuration in which around a plasma enhancedCVAD chamber (thin film formation means) 31, a load and unload (L/UL)chamber 33, a cassette station (C/S) 34, a sputtering chamber 35, and anetching chamber (etching means) 36 are provided, each being connected tothe plasma enhanced CVD chamber 31 via a gate valve 32.

[0152] In the plasma enhanced CVD chamber 31, a thin film is formed on asubstrate 1 by plasma enhanced CVD. More specifically, as shown in FIG.16, the plasma enhanced CVD chamber 31 includes a reaction chamber(reaction vessel) 38, a holder 39 for holding the substrate 1, a gassupply tube (supply portion) 40 for supplying a source gas to the insideof the reaction chamber 38, an exhaust tube 41 for exhausting gas fromthe reaction chamber 38, a halogen lamp (electromagnetic waveirradiation portion) 42 provided outside the reaction chamber 38, aviewport 43 for transmitting light generated from the halogen lamp 42,an upper electrode 44, and a lower electrode (reaction excitationportion). The viewport 43 is made, for example, of quartz or glass.

[0153] The L/UL chamber 33 transfers the substrate 1 in and out from theoutside via the gate valve 32. The cassette station 34 stores acassette. The cassette stores a plurality of the substrates 1. In thesputtering chamber 35, a thin film is formed on the substrate 1 bysputtering. In the etching chamber 36, the thin film formed on thesubstrate 1 is removed. The substrate 1 is transferred in and outbetween the chambers by a substrate transport means 37 such as a robot.

[0154] Using an apparatus for fabricating a thin film transistor havingan apparatus configuration such as that described above, a thin filmtransistor according to Example 1 was fabricated as follows.

[0155] First, a substrate 1 made of a glass substrate was transported tothe sputtering chamber 35 by the substrate transport means 37. In thesputtering chamber 35, a metal film made of Mo was coated on thesubstrate 1 by sputtering. Thereafter, the metal film was patterned in apredetermined pattern by photolithography to form a gate electrode 51.Subsequently, the substrate 1 having formed thereon the gate electrode51 was transported to the plasma enhanced CVD chamber 31 by thesubstrate transport means 37, and a gate insulating layer 52 made ofSiN_(x) was formed on the substrate 1 by plasma enhanced CVD (see FIG.17(a)).

[0156] Then, using the halogen lamp 42, light was irradiatedintermittently onto the substrate 1 from the other side of the depositedsurface. Here, the surface temperature of the gate insulating layer 52in a region above the gate electrode 51 was set to about 300° C. Inaddition, using SiH₄ gas as a source gas, an a-Si thin film was formedon the gate insulating layer 52 by plasma enhanced CVD. In the a-Si thinfilm thus formed, portions above and in the vicinity of the gateelectrode 51 had such film properties that contain few SiH₂ bonds, whileother portions had such film properties that contain numerous SiH₂bonds.

[0157] Moreover, the substrate 1 was transported to the etching chamber36 and the a-Si thin film was etched by hydrogen plasma treatment so asto selectively remove the portions with such film properties thatcontain numerous SiH₂ bonds. Thereby, as is shown in FIG. 17(b), asemiconductor thin film 53 with a predetermined pattern was formed.

[0158] Next, on the gate insulating layer 52 and the semiconductor thinfilm 53, a SiN_(x) film was formed by plasma enhanced CVD and thenpatterned by photolithography to form a channel passivation layer 54.

[0159] Subsequently, on the gate insulating layer 52, the semiconductorthin film 53, and the channel passivation layer 54, an a-Si thin film 55was formed by plasma enhanced CVD and then patterned by photolithography(see FIG. 17(c)). Further, n⁺ ions were implanted from the top of thechannel passivation layer 54, thereby forming an n⁺ a-Si thin film 55′(see FIG. 17(d)).

[0160] Then, a metal film made of Mo was coated by sputtering and thenpatterned in a predetermined pattern by photolithography to form asource electrode 56 and a drain electrode 57 (see FIG. 17(e)).

[0161] Thus, a channel passivation type thin film transistor accordingto Example 1 was fabricated.

EXAMPLE 2

[0162] Example 2 is such that a method of fabricating a thin filmaccording to the foregoing Embodiment 1 is applied to the fabrication ofa thin film transistor. Note that a thin film transistor according toExample 2 is different from a thin film transistor according to theforegoing Example 1 in that the thin film transistor is of a channeletch type. FIGS. 18(a) to 18(c) are cross-sectional views forillustrating the fabrication steps of a thin film transistor accordingto the present example.

[0163] First, in the same manner as the foregoing Example 1, a gateelectrode 51 was formed, and then further a gate insulating layer 52made of SiN_(x) was formed (see FIG. 18(a)).

[0164] Next, in the same manner as the foregoing Example 1, on the gateinsulating layer 52, an a-Si thin film was formed and then etched byhydrogen plasma treatment to form a semiconductor thin film 53 (see FIG.18(b)).

[0165] Then, on the gate insulating layer 52 and the semiconductor thinfilm 53, an a-Si thin film was formed by plasma enhanced CVD, andthereafter, n⁺ ions were implanted from the top of the a-Si thin film,thereby forming an n⁺ a-Si thin film. Further, on the n⁺ a-Si thin film,a metal film made of a Ti—Al layered film was formed Subsequently, then⁺ a-Si thin film and the metal film were patterned, byphotolithography, in a predetermined pattern so as to form an n⁺ a-Sithin film 61, a source electrode 62, and a drain electrode 63.

[0166] Moreover, a SiN_(x) layer was formed to cover the semiconductorthin film 53, the n⁺ a-Si thin film 61, the source electrode 62, and thedrain electrode 63, and then patterned by photolithography to form apassivation layer 64.

[0167] Thus, a channel etch type thin film transistor according toExample 2 was fabricated.

EXAMPLE 3

[0168] Example 3 is such that a method of fabricating a thin filmaccording to the foregoing Embodiment 2 is applied to the fabrication ofa thin film transistor.

[0169] First, in the same manner as the foregoing Example 1, a gateelectrode 51 was formed, and then further a gate insulating layer 52made of SiN_(x) was formed (see FIG. 17(a)).

[0170] Next, in the same manner as the foregoing Example 1, using ahalogen lamp, light was irradiated intermittently onto the substrate 1from the other side of the deposited surface. Here, the surfacetemperature of the gate insulating layer 52 in a region above the gateelectrode 51 was set to about 400° C. Subsequently, using Si2HG gas as asource gas, an a-Si thin film was deposited, by low-pressure CVD, onlyin regions of the gate insulating layer 52 above and in the vicinity ofthe gate electrode 51 (see FIG. 17(b)).

[0171] Then, in the same manner as the foregoing Example 1, a channelpassivation layer 54, an n⁺ a-Si thin film 55′, a source electrode 56,and a drain electrode 57 were formed (see FIG. 17(e)).

[0172] Thus, a channel passivation type thin film transistor accordingto Example 3 was fabricated.

EXAMPLE 4

[0173] Example 4 is such that a method of fabricating a thin filmaccording to the foregoing Embodiment 2 is applied to the fabrication ofa thin film transistor. Note that a thin film transistor according toExample 4 is different from a thin film transistor according to theforegoing Example 3 in that the thin film transistor is of a channeletch type.

[0174] First, in the same manner as the foregoing Example 2, a gateelectrode 51 was formed, and then further a gate insulating layer 52made of SiN_(x) was formed (see FIG. 18(a)).

[0175] Next, in the same manner as the foregoing Example 1, using ahalogen lamp, light was irradiated intermittently onto the substrate 1from the other side of the deposited surface. Here, the surfacetemperature of the gate insulating layer 52 in a region above the gateelectrode 51 was set to about 400° C. Subsequently, using Si₂H₆ gas as asource gas, an a-Si thin film was deposited, by low-pressure CVD, onlyin regions of the gate insulating layer 52 above and in the vicinity ofthe gate electrode 51 (see FIG. 18(b)).

[0176] Subsequently, in the same manner as the foregoing Example 2, onthe gate insulating layer 52 and the semiconductor thin film 53, an n⁺a-Si thin film was formed, and then on the n⁺ a-Si thin film a metalfilm made of a Ti—Al layered film was formed. Further, the n⁺ a-Si thinfilm and the metal film were patterned in a predetermined pattern byphotolithography so as to form an n⁺ a-Si thin film 61, a sourceelectrode 62, and a drain electrode 63. Moreover, a passivation layer 64was formed to cover the semiconductor thin film 53, the n⁺ a-Si thinfilm 61, the source electrode 62, and the drain electrode 63.

[0177] Thus, a channel etch type thin film transistor according toExample 4 was fabricated.

EXAMPLES 5 TO 8

[0178] Thin film transistors according to Examples 5 to 8 correspond tothin film transistors according to the foregoing Examples 1 to 4,respectively, and have the same configurations as their correspondingthin film transistors. Note, however, that the fabrication methods forthe thin film transistors according to Examples 5 to 8 are differentfrom those for the thin film transistors according to Examples 1 to 4 inthat the substrate surface was selectively heated by passing an electriccurrent through the gate electrodes, instead of irradiating light.

EXAMPLE 9

[0179] Example 9 is such that a method of fabricating a thin filmaccording to the foregoing Embodiment 1 is applied to the fabrication ofa thin film transistor. Note that a thin film transistor according toExample 9 is different from a thin film transistor according to theforegoing Example 1 in that the thin film transistor is of a top-gatetype. FIGS. 19(a) to 19(d) are cross-sectional views for illustratingthe fabrication steps of a thin film transistor according to Example 9.

[0180] First, as is shown in FIG. 19(a), a metal film made of Mo wasdeposited on a substrate 1 by sputtering. This metal film was patternedby photolithography to form a source electrode 71 and a drain electrode72.

[0181] Next, using a halogen lamp, light was irradiated intermittentlyonto the substrate 1 from the other side of the deposited surface. Here,the surface temperatures of the source electrode 71 and the drainelectrode 72 were set to about 300° C. Further, using SiH₄ gas as asource gas, an a-Si thin film was formed, by plasma enhanced CVD, on thesubstrate 1, the source electrode 71, and the drain electrode 72. In thea-Si thin film thus formed, portions covering the source electrode 71and the drain electrode 72 had such film properties that contain fewSiH₂ bonds and other portions had such film properties that containnumerous SiH₂ bonds. Moreover, n⁺ ions were implanted in the a-Si thinfilm, thereby forming an n⁺ a-Si thin film.

[0182] Subsequently, the n⁺ a-Si thin film was etched by hydrogen plasmatreatment so as to selectively remove only the portions with such filmproperties that contain numerous SiH₂ bonds. Thereby, an n⁺ a-Si thinfilm 73 with a predetermined pattern was formed.

[0183] Then, on the substrate 1 and the n⁺ a-Si thin film 73, an a-Sithin film was formed and then patterned, by photolithography, into anisland so as to have a predetermined pattern, thereby forming an a-Sithin film 74 (see FIG. 19(b)).

[0184] Subsequently, on the substrate 1 and the a-Si thin film 74, agate insulating layer 75 made of SiO₂ was formed by plasma enhanced CVDFurther, a metal film was formed on the gate insulating layer 75 andthen patterned, by photolithography, in a predetermined pattern to forma gate electrode 76 (see FIG. 19(c)). Note that in the case where thesource electrode 71 and the drain electrode 72 are self-aligned with thegate 15 electrode 76, the gate electrode 76 is formed preferably bybackside exposure such that the substrate 1 is irradiated with lightfrom the other side of the deposited surface, and by lift-off.

[0185] Finally, a passivation film 77 made of a SiN_(x) film was formedby plasma enhanced CVD (see FIG. 19(d)).

[0186] Thus, a top-gate type thin film transistor according to Example 9was fabricated.

[0187] (Results)

[0188] According to the methods of fabricating a thin film transistor ofExamples 1 to 9 described above, when forming a semiconductor thin film53 with a predetermined pattern, no mask was required and thus thenumber of masks was reduced, achieving a reduction in fabrication costs.In addition, in the foregoing Example 3 and 4, it was not necessary toetch an a-Si thin film by hydrogen plasma treatment, and therefore thenumber of fabrication steps was further reduced compared to theforegoing Examples 1 and 2.

[0189] Moreover, thin film transistors obtained in the foregoingExamples 1 to 9 had an a-Si thin film containing therein few SiH₂ bonds,and thus the thin film transistors had high mobility and high quality.Further, the a-Si thin film had few defects therein, and therefore areduction in leakage current in an OFF state was made possible.

[0190] (Miscellaneous)

[0191] Note that when a semiconductor thin film formed in apredetermined pattern in the foregoing Examples 1 and 2 was crystallizedusing excimer laser or the like, it was also possible to fabricate apolycrystalline silicon thin film transistor intended to realize anon-glass structure such as drive-circuit-on-glass. In this case too, thenumber of masks was reduced, and thus a reduction in fabrication costswas achieved.

[0192] Furthermore, the foregoing Example 9 described the case offorming an a-Si thin film; however, the present invention is not limitedthereto. It is also possible to form a p-Si film.

[0193] Industrial Applicability

[0194] As has been described above, according to the methods of thepresent invention, when forming a thin film, the entire surface of thesubstrate is not heated but only a portion of the substrate necessaryfor film formation is selectively heated, and thus a significantincrease in substrate temperature can be prevented, reducing the processtemperature.

[0195] In addition, since a thin film is formed with the substrate beingselectively heated, a film with film properties varying from region toregion is formed on the substrate. By varying the film properties,differing etching rates can be obtained, and thus even if etching isperformed under the same conditions, only portions with specified filmproperties can be selectively removed. As a result, the processing stepssuch as photolithography conventionally required can be reduced, makingit possible to reduce the number of fabrication steps and fabricationcosts.

[0196] Moreover, when a thin film is formed with the substrate beingselectively heated, differing deposition rates can be obtained, and thusit is possible to deposit a thin film only in a specified region on thesubstrate. Thus, in this case too, a lithography step conventionallyrequired when patterning a thin film can be omitted, and therefore thenumber of fabrication steps is reduced, achieving a reduction in costs.

[0197] Furthermore, semiconductor thin films fabricated according to themethods of the present invention have high mobility. Thus, when, forexample, a thin film transistor provided with such a semiconductor thinfilm is applied to a liquid crystal display device and the like, ahigh-definition device and a high-speed built-in drive circuit can beobtained. In addition, since the above-described semiconductor thinfilms have few defects, a reduction in leakage current in an OFF stateis achieved. Thus, thin film transistors provided with suchsemiconductor thin films according to the present invention haveexcellent performance and excellent reliability.

What is claimed is:
 1. A method of fabricating a thin film comprising:forming a thin film on a substrate, the thin film with film propertiesvarying from region to region on the substrate being formed byselectively heating the substrate; and patterning the thin film in apredetermined pattern by etching the thin film to selectively removeonly a portion of the thin film with specified film properties.
 2. Themethod of fabricating a thin film according to claim 1, wherein thesubstrate is selectively heated by forming, on the substrate, an energyabsorber or an energy absorber with a predetermined pattern, andsubsequently imparting energy to the energy absorber to release heatfrom the energy absorber.
 3. The method of fabricating a thin filmaccording to claim 2, wherein the energy is imparted by irradiating anelectromagnetic wave to the energy absorber.
 4. The method offabricating a thin film according to claim 1, wherein the substrate isselectively heated by forming, on the substrate, a conductive film or aconductive film with a predetermined pattern, and subsequently passingan electric current through the conductive film to release heat from theconductive film.
 5. The method of fabricating a thin film according toclaim 1, wherein the substrate is selectively heated intermittently. 6.The method of fabricating a thin film according to claim 1, wherein thestep of forming the thin film employs CVD.
 7. The method of fabricatinga thin film according to claim 5, wherein the CVD is plasma enhancedCVD.
 8. The method of fabricating a thin film according to claim 1,wherein a surface temperature of the substrate when the substrate isselectively heated is equal to or above a temperature at which a sourcegas for the thin film causes a chemical reaction.
 9. The method offabricating a thin film according to claim 1, wherein the thin film isetched by hydrogen radical treatment.
 10. A method of fabricating a thinfilm comprising: depositing a thin film on a substrate, the thin filmbeing deposited only in a specified region by selectively heating thesubstrate to vary a deposition rate from region to region on thesubstrate.
 11. The method of fabricating a thin film according to claim10, wherein the substrate is selectively heated by forming, on thesubstrate, an energy absorber or an energy absorber with a predeterminedpattern, and subsequently imparting energy to the energy absorber torelease heat from the energy absorber.
 12. The method of fabricating athin film according to claim 10, wherein the substrate is selectivelyheated by forming, on the substrate, a conductive film or a conductivefilm with a predetermined pattern, and subsequently passing an electriccurrent through the conductive film to release heat from the conductivefilm.
 13. The method of fabricating a thin film according to claim 10,wherein the substrate is selectively heated intermittently.
 14. Themethod of fabricating a thin film according to claim 10, wherein thestep of depositing the thin film employs CVD.
 15. The method offabricating a thin film according to claim 10, wherein a surfacetemperature of the substrate when the substrate is selectively heated isequal to or above a temperature at which a source gas for the thin filmcauses a chemical reaction.
 16. A method of fabricating a thin filmtransistor comprising: forming, on an insulating substrate, a metal thinfilm with a predetermined pattern; forming an insulating layer on themetal thin film; forming a semiconductor thin film on the insulatinglayer, the semiconductor thin film with film properties varying betweena region above and in the vicinity of the metal thin film and otherregions being formed by imparting energy to the metal thin film torelease the energy as heat from the metal thin film so that theinsulating layer is selectively heated; and patterning the semiconductorthin film in a predetermined pattern by etching the semiconductor thinfilm to selectively remove the other regions.
 17. The method offabricating a thin film transistor according to claim 16, wherein themetal thin film serves as a gate electrode or a source electrode and adrain electrode.
 18. The method of fabricating a thin film transistoraccording to claim 16, wherein the insulating layer is selectivelyheated by irradiating an electromagnetic wave, serving as the energy, tothe metal thin film to release heat from the metal thin film.
 19. Themethod of fabricating a thin film transistor according to claim 16,wherein the insulating layer is selectively heated by passing anelectric current through the metal thin film to release heat from themetal thin film.
 20. The method of fabricating a thin film transistoraccording to claim 16, wherein the energy is imparted to the metal thinfilm intermittently.
 21. The method of fabricating a thin filmtransistor according to claim 16, wherein the step of forming thesemiconductor thin film employs CVD.
 22. The method of fabricating athin film transistor according to claim 21, wherein the CVD is plasmaenhanced CVD.
 23. The method of fabricating a thin film transistoraccording to claim 16, wherein a surface temperature of the insulatinglayer when the insulating layer is selectively heated is equal to orabove a temperature at which a source gas for the semiconductor thinfilm causes a chemical reaction.
 24. The method of fabricating a thinfilm transistor according to claim 16, wherein the semiconductor thinfilm is etched by hydrogen radical treatment.
 25. The method offabricating a thin film transistor according to claim 16, wherein afterthe step of forming the semiconductor thin film, the semiconductor thinfilm is crystallized.
 26. The method of fabricating a thin filmtransistor according to claim 25, wherein laser annealing is performedinstead of the heat treatment.
 27. A method of fabricating a thin filmtransistor comprising: forming, on an insulating substrate, a metal thinfilm with a predetermined pattern; forming an insulating layer on themetal thin film; and depositing a semiconductor thin film on theinsulating layer, the semiconductor thin film being deposited only in aspecified region by imparting energy to the metal thin film to releasethe energy as heat from the metal thin film so that the insulating layeris selectively heated, thereby varying a deposition rate from region toregion on the insulating layer.
 28. The method of fabricating a thinfilm transistor according to claim 27, wherein the metal thin filmserves as a gate electrode or a source electrode and a drain electrode.29. The method of fabricating a thin film transistor according to claim27, wherein the insulating layer is selectively heated by irradiating anelectromagnetic wave, serving as the energy, to the metal thin film torelease heat from the metal thin film.
 30. The method of fabricating athin film transistor according to claim 27, wherein the insulating layeris selectively heated by passing an electric current through the metalthin film to release heat from the metal thin film.
 31. The method offabricating a thin film transistor according to claim 27, wherein theenergy is imparted to the metal thin film intermittently.
 32. The methodof fabricating a thin film transistor according to claim 27, wherein thestep of forming the semiconductor thin film employs CVD.
 33. The methodof fabricating a thin film transistor according to claim 27, wherein asurface temperature of the insulating layer when the insulating layer isselectively heated is equal to or above a temperature at which a sourcegas for the semiconductor thin film causes a chemical reaction.
 34. Themethod of fabricating a thin film transistor according to claim 27,wherein after the step of depositing the semiconductor thin film, thesemiconductor thin film is crystallized.
 35. A method of fabricating athin film transistor comprising: forming, on an insulating substrate, ametal thin film with a predetermined pattern; forming a firstsemiconductor thin film on the insulating substrate with the insulatingsubstrate being selectively heated by imparting energy to the metal thinfilm to release the energy as heat from the metal thin film, the firstsemiconductor thin film having film properties varying between a portioncovering the metal thin film and other portions; patterning the firstsemiconductor thin film by etching the first semiconductor thin film toselectively remove only the other portions, thereby covering only themetal thin film; forming, on the insulating substrate having the firstsemiconductor thin film thereon, a second semiconductor thin film with ahigher melting point than the first semiconductor thin film; andcrystallizing the second semiconductor thin film by heat treatment withthe first semiconductor thin film as growth nucleus.
 36. The method offabricating a thin film transistor according to claim 35, wherein themetal thin film is made of at least one type or two or more types ofmetal selected from the group consisting of Ni, Pd, Pt, Al, and Ag. 37.The method of fabricating a thin film transistor according to claim 35,wherein the first semiconductor thin film is one of an a-Ge thin filmand an a-GeSi thin film, and wherein the second semiconductor thin filmis a Si thin film.
 38. The method of fabricating a thin film transistoraccording to claim 35, wherein laser annealing is performed instead ofthe heat treatment.
 39. A method of fabricating a thin film transistorcomprising: forming, on an insulating substrate, a metal thin film witha predetermined pattern; depositing a first semiconductor thin film soas to cover the metal thin film, the fist semiconductor thin film beingdeposited only on top and side surfaces of the metal thin film, byimparting energy to the metal thin film to release the energy as heatfrom the metal thin film so that a deposition rate varies between aregion in the vicinity of the metal thin film and other regions;forming, on the insulating substrate having the first semiconductor thinfilm thereon, a second semiconductor thin film with a higher meltingpoint than the first semiconductor thin film; and crystallizing thesecond semiconductor thin film by heat treatment with the firstsemiconductor thin film as growth nucleus.
 40. The method of fabricatinga thin film transistor according to claim 39, wherein the metal thinfilm is made of at least one type or two or more types of metal selectedfrom the group consisting of Ni, Pd, Pt, Al, and Ag.
 41. The method offabricating a thin film transistor according to claim 39, wherein thefirst semiconductor thin film is one of an a-Ge thin film and an a-GeSithin film, and wherein the second semiconductor thin film is a Si thinfilm.
 42. The method of fabricating a thin film transistor according toclaim 39, wherein laser annealing is performed instead of the heattreatment.
 43. A method of fabricating a thin film transistorcomprising: forming, on an insulating substrate, a metal thin film witha predetermined pattern; forming an insulating layer on the insulatingsubstrate having the metal thin film thereon; forming a firstsemiconductor thin film on the insulating layer, the first semiconductorthin film with film properties varying from region to region on theinsulating layer being formed by imparting energy to the metal thin filmto release the energy as heat from the metal thin film so that theinsulating layer is selectively heated; patterning the firstsemiconductor thin film in a predetermined pattern by etching the firstsemiconductor thin film to selectively remove only a portion of thefirst semiconductor thin film with specified film properties; forming,on the insulating substrate having the first semiconductor thin filmthereon, a second semiconductor thin film with a higher melting pointthan the first semiconductor thin film; and crystallizing the secondsemiconductor thin film by heat treatment with the first semiconductorthin film as growth nucleus.
 44. The method of fabricating a thin filmtransistor according to claim 43, wherein the metal thin film is made ofat least one type or two or more types of metal selected from the groupconsisting of Ni, Pd, Pt, Al, and Ag.
 45. The method of fabricating athin film transistor according to claim 43, wherein the firstsemiconductor thin film is one of an a-Ge thin film and an a-GeSi thinfilm, and wherein the second semiconductor thin film is a Si thin film.46. The method of fabricating a thin film transistor according to claim43, wherein laser annealing is performed instead of the heat treatment.47. A method of fabricating a thin film transistor comprising: forming,on an insulating substrate, a metal thin film with a predeterminedpattern; forming an insulating layer on the insulating substrate havingthe metal thin film thereon; depositing a first semiconductor thin filmon the insulating layer, the first semiconductor thin film beingdeposited only in a specified region by imparting energy to the metalthin film to release the energy as heat from the metal thin film so thatthe insulating layer is selectively heated, thereby varying a depositionrate from region to region on the insulating layer; forming, on theinsulating substrate having the first semiconductor thin film thereon, asecond semiconductor thin film with a higher melting point than thefirst semiconductor thin film; and crystallizing the secondsemiconductor thin film by heat treatment with the first semiconductorthin film as growth nucleus.
 48. The method of fabricating a thin filmtransistor according to claim 47, wherein the metal thin film is made ofat least one type or two or more types of metal selected from the groupconsisting of Ni, Pd, Pt, Al, and Ag.
 49. The method of fabricating athin film transistor according to claim 47, wherein the firstsemiconductor thin film is one of an a-Ge thin film and an a-GeSi thinfilm, and wherein the second semiconductor thin film is a Si thin film.50. The method of fabricating a thin film transistor according to claim47, wherein laser annealing is performed instead of the heat treatment.51. An apparatus for fabricating a thin film comprising: a metal thinfilm formation means for forming, on a substrate, a metal thin film witha predetermined pattern; a thin film formation means for forming a thinfilm on the substrate, the thin film with film properties varying fromregion to region on the substrate being formed by imparting energy tothe metal thin film to release the energy as heat from the metal thinfilm so that the substrate is selectively heated; and an etching meansfor patterning the thin film in a predetermined pattern by etching thethin film to selectively remove only a portion of the thin film withspecified film properties.
 52. The apparatus for fabricating a thin filmaccording to claim 51, wherein the thin film formation means comprising:a reaction vessel for holding the substrate inside; an electromagneticwave irradiation portion for irradiating an electromagnetic wave,serving as the energy, to the metal thin film; a supply portion forsupplying a source gas to an inside of the reaction vessel; and areaction excitation portion for exciting a chemical reaction of thesource gas.
 53. The apparatus for fabricating a thin film according toclaim 51, wherein an electric current application portion forintermittently passing an electric current through the metal thin filmis provided, in place of the electromagnetic wave irradiation portion.54. The apparatus for fabricating a thin film according to claim 51,wherein the reaction excitation portion is a plasma excitation portion.55. An apparatus for fabricating a thin film comprising: a metal thinfilm formation means for forming, on a substrate, a metal thin film witha predetermined pattern; and a thin film formation means for forming athin film on the substrate, the thin film being formed only in aspecified region by imparting energy to the metal thin film to releasethe energy as heat from the metal thin film so that the substrate isselectively heated, thereby varying a deposition rate from region toregion on the substrate.
 56. The apparatus for fabricating a thin filmaccording to claim 55, wherein the thin film formation means comprising:a reaction vessel for holding the substrate inside; an electromagneticwave irradiation portion for irradiating an electromagnetic wave,serving as the energy, to the metal thin film; a supply portion forsupplying a source gas to an inside of the reaction vessel; and areaction excitation portion for exciting a chemical reaction of thesource gas.
 57. The apparatus for fabricating a thin film according toclaim 55, wherein an electric current application portion forintermittently passing an electric current through the metal thin filmis provided, in place of the electromagnetic wave irradiation portion.58. The apparatus for fabricating a thin film according to claim 55,wherein the reaction excitation portion is a plasma excitation portion.59. A thin film transistor comprising; a metal thin film having apredetermined pattern and provided on an insulating substrate; aninsulating layer provided on the insulating substrate having the metalthin film thereon; and a semiconductor thin film having a predeterminedpattern and provided on the insulating layer, wherein the semiconductorthin film is patterned in the predetermined pattern by forming thesemiconductor thin film by imparting energy to the metal thin film torelease the energy as heat from the metal thin film so that theinsulating layer is selectively heated, thereby varying film propertiesbetween a region above and in the vicinity of the metal thin film andother regions, and subsequently etching the semiconductor thin film toselectively remove the other regions.
 60. The thin film transistoraccording to claim 59, wherein a sidewall of the semiconductor thin filmhas a gently sloping surface.
 61. A thin film transistor comprising: ametal thin film having a predetermined pattern and provided on aninsulating substrate; an insulating layer provided on the insulatingsubstrate having the metal thin film thereon; and a semiconductor thinfilm having a predetermined pattern and provided on the insulatinglayer, wherein the semiconductor thin film is deposited only in aspecified region by imparting energy to the metal thin film to releasethe energy as heat from the metal thin film so that the insulating layeris selectively heated, thereby varying a deposition rate from region toregion on the insulating layer.
 62. The thin film transistor accordingto claim 61, wherein a sidewall of the semiconductor thin film has agently sloping shape.
 63. A thin film transistor comprising: a metalthin film patterned on an insulating substrate in a predeterminedpattern; a first semiconductor thin film deposited so as to cover themetal thin film, the first semiconductor thin film being provided so asto cover only the metal thin film, by imparting energy to the metal thinfilm to release the energy as heat from the metal thin film, therebyproviding the first semiconductor thin film with film properties varyingbetween a portion covering the metal thin film and other regions, andsubsequently selectively removing the other portions by etching; and asecond semiconductor thin film provided on the insulating substratehaving the first semiconductor thin film thereon, and having a highermelting point than the first semiconductor thin film, the secondsemiconductor thin film being crystallized by heat treatment with thefirst semiconductor thin film as growth nucleus, wherein a region of thecrystallized second semiconductor thin film not having the firstsemiconductor thin film serves as a channel portion.
 64. A thin filmtransistor comprising: a metal thin film patterned on an insulatingsubstrate in a predetermined pattern; a first semiconductor thin filmdeposited so as to cover the metal thin film, the first semiconductorthin film being deposited on top and side surfaces of the metal thinfilm, by imparting energy to the metal thin film to release the energyas heat from the metal thin film so that a deposition rate variesbetween a region in the vicinity of the metal thin film and otherregions; and a second semiconductor thin film provided on the insulatingsubstrate having the first semiconductor thin film thereon, and having ahigher melting point than the first semiconductor thin film, the secondsemiconductor thin film being crystallized by heat treatment with thefirst semiconductor thin film as growth nucleus, wherein a region of thecrystallized second semiconductor thin film not having the firstsemiconductor thin film serves as a channel portion.
 65. A thin filmtransistor comprising: a metal thin film patterned on an insulatingsubstrate in a predetermined pattern; an insulating layer provided onthe insulating substrate having the metal thin film thereon; a firstsemiconductor thin film formed on the insulating layer with theinsulating layer being selectively heated by imparting energy to themetal thin film to release the energy as heat from the metal thin film,thereby varying film properties of the first semiconductor thin filmbetween a portion corresponding to a region with a high surfacetemperature of the insulating layer and a portion corresponding to aregion with a low surface temperature of the insulating layer, the firstsemiconductor thin film being provided only in the region with a highsurface temperature, by etching the first semiconductor thin film toselectively remove the portion corresponding to the region with a lowsurface temperature; and a second semiconductor thin film provided onthe insulating substrate having the first semiconductor thin filmthereon, and having a higher melting point than the first semiconductorthin film, the second semiconductor thin film being crystallized by heattreatment with the first semiconductor thin film as growth nucleus,wherein a region of the crystallized second semiconductor thin film nothaving the first semiconductor thin film serves as a channel portion.66. A thin film transistor comprising: a metal thin film patterned on aninsulating substrate in a predetermined pattern; an insulating layerprovided on the insulating substrate having the metal thin film thereon;a first semiconductor thin film provided on the insulating layer, theinsulating layer selectively heated by imparting energy to the metalthin film to release the energy as heat from the metal thin film so thata deposition rate varies between a region with a high surfacetemperature of the insulating layer and a region with a low surfacetemperature of the insulating layer, thereby providing the firstsemiconductor thin film only in the region with a high surfacetemperature; and a second semiconductor thin film provided on theinsulating substrate having the first semiconductor thin film thereon,and having a higher melting point than the first semiconductor thinfilm, the second semiconductor thin film being crystallized by heattreatment with the first semiconductor thin film as growth nucleus,wherein a region of the crystallized second semiconductor thin film nothaving the first semiconductor thin film serves as a channel portion.